This project (1) examines cancer incidence and mortality among populations exposed to ionizing and non-ionizing radiation, especially at low dose levels; (2) characterizes the risk of radiation-induced cancer in terms of tissues at risk, dose response, radiation quality, temporal distribution of dose, time since exposure, age at exposure and at observation, and possible modifying influences of other environmental and host factors; and (3) examines, tests, and formulates models of radiation carcinogenesis to help define basic mechanisms. Group studies include the Japanesse A-bomb survivors, and several large populations with documented therapeutic (e.g., cervical cancer patients), diagnostic (e.g., tuberculosis patients), and occupational (e.g., x-ray technologists) exposures to ionizing radiation. Program members serve on committees advising the Government as well as international agencies. Results of studies suggest that: (1) the risk of radiogenic cancer remains throughout life; (2) large doses to limited volumes of some sites, such as the rectum, may induce cancer; (3) ovarian damage caused by radiation may lower breast cancer risk, even among post-menopausal women; (4) repeated relatively low radiation doses pose some future risk of breast cancer; (5) susceptibility to radiogenic breast cancer declines with increasing age at exposure, and children under age 10 are at high risk; (6) children irradiated for benign conditions of the head and neck are at high risk of developing thyroid neoplasia; (7) chromosome aberrations following partial-body irradiation persist in circulating lymphocytes for over 40 years; (8) prenatal x-ray in twins increases the risk of childhood cancer; (9) the risk of developing a second cancer following treatment for a childhood cancer reaches 12% after 25 years; (10) women treated with high-dose radioactive iodine may not be at increased risk of dying from cancer; (11) childhood cancer mortality in Utah may not be associated with radioactive fallout from nuclear weapons testing.